APACHE II Score Calculator

Calculate the APACHE II Score to estimate ICU mortality risk in critically ill patients. Enter physiologic measurements including temperature, mean arterial pressure, heart rate, respiratory rate, oxygenation (FiO2/PaO2), arterial pH, serum sodium, serum potassium, serum creatinine, hematocrit, WBC, Glasgow Coma Score, age, and chronic health status. Your result includes the total APACHE II score and the estimated hospital mortality percentage.

years
°C

Use rectal temperature in degrees Celsius

mmHg
bpm
breaths/min
%

Fraction of inspired oxygen (21% = room air)

mmHg

Arterial oxygen pressure — used when FiO2 < 50%

mmHg

Alveolar-arterial oxygen gradient — used when FiO2 ≥ 50%

mEq/L
mEq/L
mg/dL

Doubles creatinine score if acute renal failure is present

%
×10³/mm³

Score from 3 (worst) to 15 (normal). Points = 15 - GCS.

Liver, cardiovascular, respiratory, renal failure, or immunocompromised

Results

APACHE II Score

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Estimated Hospital Mortality

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Acute Physiology Score (APS)

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Age Points

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Chronic Health Points

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APACHE II Score Breakdown

Frequently Asked Questions

What is the APACHE II score used for?

The APACHE II (Acute Physiology and Chronic Health Evaluation II) score is a severity-of-illness scoring system used in ICUs. It estimates the risk of hospital mortality based on physiologic measurements, age, and chronic health conditions. Higher scores indicate greater disease severity and higher predicted mortality.

What is the range of the APACHE II score?

The APACHE II score ranges from a minimum of 0 to a maximum of 71 points. A score of 0 indicates minimal physiologic derangement, while scores above 35 are associated with very high predicted hospital mortality. Most patients have scores between 5 and 40.

How is APACHE II mortality calculated?

The estimated mortality is calculated using the logistic regression formula: ln(R/1-R) = -3.517 + (0.146 × APACHE II points) + 0.603 (if emergency surgery) + admission diagnosis weight. This gives a predicted probability of hospital death based on the total score and clinical context.

How is the oxygenation component scored in APACHE II?

If FiO2 is less than 50%, scoring is based on PaO2 alone. If FiO2 is 50% or greater, scoring uses the alveolar-arterial oxygen gradient (A-aDO2). A larger A-aDO2 gradient indicates worse oxygenation and results in a higher point score.

What counts as chronic organ insufficiency for APACHE II?

Chronic health points are awarded if the patient has severe organ insufficiency (hepatic, cardiovascular, renal, or respiratory) or is immunocompromised. Non-operative or emergency post-operative patients receive 5 points, while elective post-operative patients receive 2 points for this category.

How does acute renal failure affect the APACHE II creatinine score?

If the patient has acute renal failure (as opposed to chronic renal insufficiency), the creatinine score is doubled. This reflects the additional severity and mortality risk associated with acute kidney injury in critically ill patients.

Can APACHE II be used throughout a patient's hospital stay?

Yes. Unlike some scoring systems that are used only at admission, APACHE II can be applied throughout the patient's hospital course. Recalculating the score over time can help monitor disease progression and response to treatment in ICU patients.

What are the limitations of the APACHE II score?

APACHE II was developed in the 1980s and may not accurately reflect mortality risk with modern ICU treatments. It does not account for specific diagnoses equally well, can vary based on data collection methods, and should always be interpreted in the full clinical context rather than used as the sole decision-making tool.

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